Varicella-zoster virus (VZV) initiates primary infection by upper respiratory mucosal inoculation, causing varicella. VZV persists in sensory ganglia and reactivation from latency may result in zoster. The VZV genome has at least 71 known or predicted open reading frames (ORFs) but understanding how these gene products function in virulence is difficult because VZV is highly human-specific. We have addressed this obstacle by investigating VZV infection of human skin, T cell and dorsal root ganglia xenografts in the severe combined immunodeficiency (SCID) mouse model. Together with clinical observations, this work supports a new paradigm of VZV pathogenesis that incorporates a critical role for T cells as a vehicle for VZV delivery to both skin and neuronal sites of latency. VZV infects human tonsil T cells very efficiently and infected tonsil T cells transfer VZV into skin xenografts, where lesion formation occurs gradually against a barrier of a potent innate epidermal cell response. VZV-infected T cells also exit from the circulation into DRG xenografts, indicating that VZV can reach neurons by this mechanism. T cell tropism is an important difference between the life cycles of VZV and herpes simplex viruses 1 and 2. We propose state of the art screening methods to show how takeover of T cells by VZV modifies cell protein synthesis and activation and alters T cell gene regulation in combination with experiments to define how specific VZV gene products function to achieve these changes in the infected T cell. We will investigate VZV effects on T cell signaling pathways, T cell protein synthesis and T cell gene expression at single cell level using validated screening techniques that have been applied to studies of human T cell biology; methods will include multiparameter flow cytometric analysis of phosphoproteins, multiplex cytokine/chemokine assays and microfluidics-based profiling of gene expression (Aim 1). Based on our preliminary observations, we will examine the contributions of three VZV proteins, immediate early 4 (IE4), immediate early 62 (IE62) and ORF3 protein to VZV T cell tropism (Aim 2). Screening experiments that identify major VZV-induced consequences for the T cell will set the stage for additional studies of the mechanisms by which the virus achieves these effects. VZV is likely to target some pathways common to other T cell tropic viruses and strategies for applying new technologies to investigate viral pathogenesis should emerge. From a public health perspective, this work should provide information to improve the live attenuated Oka strain vaccines for varicella and zoster. While these vaccines are safe and beneficial, this work will be relevant for developing a 2nd generation VZV vaccine which consists of a VZV recombinant virus that has impaired T cell tropism and therefore less potential to disseminate in high risk patients and to establish latency in healthy individuals.